Pneumatic tires offer high load capacity per unit mass, along with a large contact area and relatively low vertical stiffness. High contact area results in the ability to both efficiently generate high tangential forces and obtain excellent wear characteristics. However, pneumatic tires are also prone to flats. Well known in the patent literature, non-pneumatic tires offer flat-free operation, yet generally contain some compromise.
Higher cost is often associated with non-pneumatic tires when complex assemblages of composite materials are used. Related to this, production methodologies can be laborious. For example, U.S. Pat. No. 7,201,194 discloses a non-pneumatic tire containing an annular band which is comprised of at least two inextensible membrane-like reinforcing layers, which are separated by an elastomeric layer. This annular band is then affixed to a central wheel via flexible spokes in a web design. This composite composition suggests a complex manufacturing process. High production costs could be involved.
Conversely, U.S. Pat. No. 6,615,885 discloses a non-pneumatic tire that can be fabricated without composite reinforcement. The design consists of a rim connected to a hub via curved spokes. The spokes are sufficiently rigid such that loads are transmitted via bending. Such a structure works acceptably well for very small tires and low loads; however, one skilled in the art of non-pneumatic structures can show that this technological approach would result in high tire mass for applications supporting higher loads in larger-scale applications.
U.S. Pat. No. 7,013,939 discloses a non-pneumatic tire consisting of a simple elastomeric band, a hub, and connecting spokes which act primarily in tension. As with U.S. Pat. No. 6,615,885, this solution works for very small tires and low loads. However, at higher loads with larger tire dimensions, one skilled in the art of non-pneumatic tire design can show that the contact area characteristics become strongly degraded. This would result in a loss of performance.
US Patent Application US2012/0234444 A1 discloses a non-pneumatic tire with an annular reinforcing web, made of a homogeneous material. However, the disclosed structure supports load via compression. The generally radial spokes are thick and designed to act as columns under normal operation. Thus, the distance between the outer tire diameter and the rigid wheel diameter must be relatively small, in order to resist buckling under high loads. Therefore, the absorbed energy potential—a principle virtue of the pneumatic tire—may be limited in this tire design.
Finally, U.S. Pat. No. 8,517,068 B2 discloses a resilient wheel that operates similarly to the invention of U.S. Pat. No. 7,201,194, except that the circumferential membranes are connected by discrete cylindrical support elements. Here, the advantages could include lower weight and the ability to overcome temperature limitations associated with elastomers. However, the assemblage of these disparate elements could be laborious and expensive.
The present invention breaks these compromises by disclosing a non-pneumatic tire that, in a preferred embodiment, can be constructed from a single homogeneous material, is light-weight, capable of large deflection, and obtains a large, constant pressure contact area. Structure geometries and non-linear material properties are disclosed that accomplish the same function as more complicated designs of prior art. In particular, prior art often employs reinforcements that behave like inextensible membranes, as well as sandwich composite constructions. Conversely, the present design is elastomeric, has no membrane-like behavior, and contains no reinforcement. While the invention has elegant simplicity, the principles of operation are not readily apparent to one of ordinary skill in the art of tire design.
While having potentially complex features, the geometries disclosed in the present invention are generally suitable for realization in the thermoplastic injection, cast, or reaction injection molding process. These practical attributes result in lower cost when produced in large volume, yet do not come at the expense of the aforementioned primary performance attributes of a pneumatic tire.
Second stage processes can be applied to this invention. For example, a non-pneumatic tire with a thermoplastic material can be designed, per procedures disclosed in this application. Then, a tread material and tread pattern can be affixed to a radially exterior extent of the annular beam. This can be accomplished via retreading procedures, by a 2nd stage injection process, or by co-injection.